This disclosure relates to a fusing system that includes a variable-nip pressure member that can be selectively modified in order to modify the dwell time for a given fusing member configuration and set temperature which enables the rapid optimization of fix and gloss for a given toner image (i.e. image type such as text, full pictorial, etc.) on a given substrate or media.
In the art of xerography or other similar image reproducing arts, a latent electrostatic image is formed on a charge-retentive surface, i.e., a photoconductor or photoreceptor. To form an image on the charge-retentive surface, the surface is first provided with a uniform charge after which it is exposed to a light or other appropriate image of an original document to be reproduced. The latent electrostatic image thus formed is subsequently rendered visible by applying any one of numerous toners specifically designed for this purpose.
It should be understood that for the purposes of the present disclosure, the latent electrostatic image may be formed by means other than by the exposure of an electrostatically charged photosensitive member to a light image of an original document. For example, the latent electrostatic image may be generated from information electronically stored or generated, and this information in digital form may be converted to alphanumeric images by image generation electronics and optics. The particular method by which the image is formed is not critical to the present disclosure, and any such suitable method may be used.
In a typical xerographic device, the toner image formed is transferred to an image receiving substrate such as paper. After transfer to the image receiving substrate, the image is made to adhere to the substrate using a fuser apparatus. To date, the use of simultaneous heat and contact pressure for fusing toner images has been the most widely accepted commercially, the most common being systems that utilize a pair of pressure engaged, members, i.e. rolls or belts.
The use of pressure engaged rolls for fixing toner images is well known in the art. See, for example, U.S. Pat. Nos. 6,289,587, 5,998,761, 4,042,804 and 3,934,113.
At the time of initial set-up of a xerographic device, the fuser system is set to be within certain specifications. Some of these specifications include nip, load, and speed. Other parameters of the fuser system include dwell time, pressure, and creep. Dwell time (nip width/process speed) is one of the more significant drivers of image fix and quality. Changes in process speed may be made in response to incoming job media type and image percent (%) area coverage. Creep, which is the release surface's % extension in the nip, is important with respect to enabling self-stripping of the paper from the fuser member. Low area coverage (text) images may require only low levels of creep, while high area coverage images require higher levels of creep to self-strip from the fusing member.
Once initially set, the nip width of a typical fuser is not changed during operation of the xerographic device. Unfortunately, several internal and external factors can cause the fuser system to drift outside of the designated specifications. For example, in a typical soft-on-hard roll pair in which the soft roll is the driving roll, the fuser system may begin operating outside of specifications due to, e.g., hardening of the roll materials over time. Typical fuser roll systems include some materials such as silicone materials that tend to become harder or softer over time at unpredictable rates. This hardening causes large reductions in both dwell time and potentially creep, which causes premature failure (e.g., smaller nip widths that lead to insufficient fixing of the toner image and/or poor image quality, as well as to poor stripping of the image receiving substrate).
In addition to these failure modes, it is at times desired that the nip width in a fuser be altered on demand. For instance, the fusing quality on thick paper is improved with large nip widths, and the fusing quality on thin papers is often improved with small nip widths. The fusing latitude in the presence of varied media and images, therefore, is improved if the nip width can be accurately set, controlled, and adjusted.
Typically, resetting the nip width to improve fusing latitude or to compensate for system failures due to the fuser system falling out of specifications has been dealt with by either (a) having a technician re-set the nip on site and/or (b) setting the nip width far above specifications at the factory, permitting the device to operate longer before falling out of specification. However, each of these ‘solutions’ has serious problems. Using technicians to reset the nip requires an on site visit by a technician and down time of the device. Initially setting the nip width high above specifications usually causes paper handling and stripping issues, especially with lightweight papers.
Optimal fusing of toner images requires the correct combination of fuser temperature, pressure, and time (dwell) in the nip which is heavily influenced by the media properties (weight, roughness, coating, thermal conductivity, etc.). The ideal fusing system would have the ability to instantaneously adjust these parameters to match media and image characteristics while maintaining xerographic process speeds. The current method to accommodate fusing of a wide range of media is to change the speed of the paper path (loss in productivity) and/or change the temperature (life reduction and time consuming) of the fuser. Any decrease in productivity or increase in idle time is considered a customer dis-satisfier and to be avoided.
A fuser system, in particular its pressure member, optimized for heavy weight or thick papers is very different than one optimized for light weight or thin papers. Heavy weight papers require longer dwells, but also require lower image-side creep due to their increased beam strength. Light papers do not require long dwells, but do require high image-side creep. Therefore, a fuser optimized for thin papers would have a relatively hard pressure member, producing high fuser member creep but small dwells, while a fuser optimized for thick papers would have a relatively soft pressure member, producing long dwells but low fuser member creep. Current fusers, especially for color machines, cannot produce the nip conditions to simultaneously support both thin and thick papers at speeds beyond 100 ppm, without resorting to temperature changes, speed changes, or load changes.